For patients with both cochlear and vestibular sensory loss, a hybrid cochlear/vestibular implant offers significant advantages over single modality prostheses that address only cochlear or only vestibular function. Cochlear and vestibular sensory loss frequently occur together, because hair cells in both parts of the inner ear are similarly sensitive to ototoxic drug exposure, Ménière's disease, infection, trauma, genetic defects and other diseases. Currently available cochlear implants (e.g., in U.S. Pat. Nos. 4,532,930; 4,592,359; 4,947,844; 5,776,172; and 6,067,474) can restore auditory sensation, and a single-modality vestibular prosthesis (e.g., in U.S. Pat. No. 6,546,291) can provide artificial vestibular sensation; however, patients with combined loss of hearing and vestibular sensation currently have no effective therapeutic options. While disability due to loss of vestibular sensation varies widely, patients may be severely affected by chronic disequilibrium and oscillopsia (visual field movement during head movements) that impede activities of daily life. The vestibular nerve should be intact in most cochlear implantation candidates with loss of vestibular sensation. In these patients, a hybrid cochlear/vestibular implant can selectively stimulate all branches of the auditory-vestibular (eighth cranial) nerve, restoring hearing and normalizing gaze- and posture-stabilizing reflexes and perception of spatial orientation.
Presently available implantable stimulation devices, such as a cochlear implant device or a neural stimulator, typically have an implanted unit, an external ac coil, and an external control unit and power source. The external control unit and power source includes a suitable control processor and other circuitry that generates and sends the appropriate command and power signals to the implanted unit to enable it to carry out its intended function. The external control unit and power source are powered by a battery that supplies electrical power through the ac coil to the implanted unit via inductive coupling for providing power for any necessary signal processing and control circuitry and for electrically stimulating select nerves or muscles. Efficient power transmission through a patient's skin from the external unit to the implanted unit via inductive coupling requires constant close alignment between the two units.
Representative prior art cochlear implant systems are disclosed, e.g., in U.S. Pat. Nos. 4,532,930; 4,592,359; 4,947,844; 5,776,172; and 6,067,474; all of which are incorporated herein by reference in their entireties.
Disadvantageously, each of the known prior art cochlear stimulation systems requires the use of an external power source and speech processing system, coupled to the implanted stimulation device. For many patients, achieving and maintaining the required coupling between the external components and the implanted component can be troublesome, inconvenient, and unsightly. Thus, there existed a need and desire for a small, lightweight fully implantable device or system that does not require an external unit in order to be fully functional, that does not need constant external power, and that includes a long-lasting internal battery that may be recharged, when necessary, within a relatively short time period.
This and other needs were satisfied by the development of fully implantable cochlear implant systems such as that disclosed by U.S. Pat. No. 6,272,382, incorporated herein by reference in its entirety. A fully implantable cochlear implant system includes at least three main modules, including (1) a small implantable cochlear stimulator (ICS) module, with permanently attached cochlear electrode array; (2) an implantable speech processor (ISP) module, with integrated microphone and rechargeable battery; and (3) an external module.
All of the prior art cochlear implant systems currently available provide significant benefits to patients who wish to hear. A significant percentage of these patients implanted with cochlear stimulation systems suffer from balance deficiencies originating in the vestibular system. Recently, others have attempted to treat balance deficiencies through a variety of different modalities, including stimulating the vestibular system. Representative vestibular stimulation systems are taught in U.S. Pat. Nos. 6,546,291 (the '291 patent); 6,219,578 (the '578 patent); 6,063,046 (the '046 patent); and 5,919,149 (the '149 patent); all of which are incorporated herein by reference in their entireties.
In the '291 patent issued on Apr. 8, 2003, Merfeld, et al. teach a balance prosthesis that provides information indicative of a patient's spatial orientation to the patient's nervous system. This is done by placing 3 rotational accelerometers in mutually orthogonal cardinal X Y and Z planes to measure roll, pitch and yaw of the head (see, '291 Merfeld patent at column 4 line 35). In the '578 patent issued on Apr. 17, 2001, Collins, et al. teach transcutaneous electrical stimulation of the vestibular system in order to modify a patient's postural sway. In the '046 patent issued on May 16, 2000, Allum teaches a method and apparatus for the diagnosis and rehabilitation of abnormal human balance corrections. And, in the '149 patent issued on Jul. 6, 1999, Allum teaches a method and apparatus for the diagnosis and rehabilitation of abnormal human postural sway.
As exemplified above, there are systems for treating hearing deficiencies and balance deficiencies separately. However, there is no single system currently available for simultaneously treating patients with both hearing and balance deficiencies. Therefore, a need exists for an invention that treats cochlear implant patients affected by balance disorders related to vestibular hypofunction and malfunction.